1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a Home Location Server (HLS) and method of processing an incoming real-time call to a mobile station (MS) in a hybrid radio telecommunications network having both second generation and third generation service nodes.
2. Description of Related Art
In radio telecommunications, the term xe2x80x9csecond generationxe2x80x9d (2G) refers to legacy circuit-switched networks, and xe2x80x9cthird generationxe2x80x9d (3G) refers to new packet-switched networks generally operating with the Internet Protocol (IP) and providing a full range of data and real-time applications such as voice, video, and other multimedia applications. During the time period that 3G.IP networks are being phased in, networks will operate with some areas of 2G only coverage, some areas of 3G only coverage, and some areas where both 2G coverage and 3G coverage are available. Most of the mobile stations (MSs) operating in such hybrid radio telecommunications networks will be capable of operating in both 2G circuit-switched service nodes and 3G packet-switched service nodes. Therefore, an MS may roam between 2G Mobile Switching Centers (MSCs), 3G Call State Control Functions (CSCFs), and, in General Packet Radio Service (GPRS) networks, between 2G Serving GPRS Support Nodes (SGSNs) and 3G SGSNs. All such nodes are referred to generically herein as xe2x80x9cswitchesxe2x80x9d.
When processing a call to an MS in a hybrid network, the call is first received in an originating switch. The switch determines the location of the called MS by sending a location request to the MS""s associated Home Location Register (HLR). The response of the HLR is dependent on whether the called MS is being served by a 2G switch such as an MSC, or whether it is being served by a 3G switch such as a CSCF. This is because there are some 3G functions and procedures that are not applicable to the 2G environment, and it is desirable for the HLR to download only what is pertinent to the serving switch. For example, if the MS is roaming in a 2G MSC, and the HLR is interrogated for location information for the MS, the HLR should return a roaming number to the interrogating switch. On the other hand, if the MS is roaming in a 3G CSCF, the HLR should return an IP address for the 3G CSCF when the HLR is interrogated.
When the called MS is roaming in a 2G MSC, the identity of the serving MSC is sent to the HLR when the MS first registers in the MSC""s service area. The HLR knows from the identity of the MSC that it is a 2G switch. Therefore, when the HLR is interrogated for location information for the called MS, the HLR knows to return a roaming number to the interrogating switch. Hence, the HLR requests a roaming number from the serving MSC for that purpose, and returns the roaming number to the interrogating switch. Likewise, if the called MS is roaming in a 3G CSCF, the identity of the serving CSCF is sent to the HLR when the MS first registers in the CSCF""s service area. The HLR knows from the identity of the CSCF that it is a 3G switch. Therefore, the HLR knows to return the IP address of the serving CSCF to any switch that interrogates the HLR for location information for the called MS.
A problem arises, however, when the MS is roaming in an SGSN in a GPRS network. Second generation SGSNs support only data applications while 3G SGSNs support both data and some real-time applications (with the exception of IP telephony which is only supported by CSCFs). An internal software upgrade converts a 2G SGSN to a 3G SGSN, but the registration message that is sent to the HLR when an MS registers there is the same. Thus, the HLR currently has no way to know whether the serving SGSN is a 2G SGSN or a 3G SGSN, and no way to determine the correct response to a location request. When the MS is in a 2G SGSN, the HLR should return a roaming number in response to a location request, while an IP address should be returned when the MS is in a 3G SGSN.
In one aspect, the present invention is a method of processing an incoming real-time call to an MS in a hybrid radio telecommunications network having both second generation (2G) and third generation (3G) service nodes. The method begins when a request for location information for the called MS is received in a Home Location Server (HLS) from an interrogating switch where the incoming call originated. The method includes the steps of determining by the HLS, whether the called MS is located in a 2G MSC or a 3G CSCF, and concluding that the called MS is located in an SGSN if the called MS is not located in either a 2G MSC or a 3G CSCF. This is followed by determining whether the SGSN is a 2G SGSN or a 3G SGSN, and informing the interrogating switch that the MS is not available for the real-time call, upon determining that the SGSN is a 2G SGSN. Upon determining that the SGSN is a 3G SGSN, the HLS orders the SGSN to page the MS and determine whether the MS accepts the incoming call. If the call is accepted, the MS performs a timely application level registration with a serving CSCF. Accordingly, the location of the subscriber is then set in the HLS. The HLS then sends the address of the serving CSCF to the interrogating switch.
In another aspect, the present invention is an HLS for processing an incoming real-time call to an MS in a hybrid radio telecommunications network having both 2G and 3G service nodes. The HLS includes control logic for receiving a request for location information for the called MS from an interrogating switch where the incoming call originated. A subscriber profile includes location information for the called MS, and a 3G flag that is set when the MS registers in a 3G SGSN. A 2G/3G location function accesses the subscriber profile to determine whether the called MS is located in a 2G MSC, a 3G CSCF, a 2G SGSN, or a 3G SGSN. The HLS also includes 2G call processing logic that performs 2G call processing procedures when the 2G/3G location function determines that the called MS is located in a 2G MSC, and 3G call processing logic that performs 3G call processing procedures when the 2G/3G location function determines that the called MS is located in a 3G CSCF or 3G SGSN.